1. Field of the Invention
The present invention relates to a signal modulation loop for the multi-mode mobile communication. The adaptive up-conversion modulation loop is used for performing the signal modulation so as to accomplish the signal modulation for the multi-mode mobile communication.
2. Description of the Prior Art
As the mobile phone gets more popular, the communication between the people gets more convenient. Not only the distance of the communication is shortened, but also the speed and efficiency for the proceeding of work are increased. Because of this, the capital and human resource are continuously invested in the development and application of the mobile communication so as to obtain the better quality and service of the communication.
In order to make the transmission speed of the mobile communication faster and the service quality better, a great amount of capital and research effort is invested, and the communication transmission protocol is developed from the first generation, the American mobile phone system (AMPS), to the popularly used second generation, the global system for mobile communication (GSM). Even the mobile phone applying the third generation protocol, the code division multiple access (CDMA), is developed and appeared in the market. All of these protocols are provided for the user to make the communication faster and have more various services. However, during the transition from one generation to another, the signal transmission and modulation between the different communication protocols become the crucial points of the development and research. Therefore, the multi-mode or multi-band signal transceiver is the main subject to be developed and researched for the wireless communication.
The conventional multi-mode adaptive up-conversion modulation loop is composed of a direct digital synthesizer, (DDS), a phase locked loop (PLL), a phase demodulator, a phase comparator and a control amplifier. Please refer to FIG. 1. FIG. 1 is a perspective diagram of a prior art modulation loop. The input modulation signal Mod is inputted into the phase comparator 10, and is compared with the modulation signal outputted by the phase demodulator 11 so as to obtain a difference. This difference is used for controlling the direct feed-in path of an assistant control amplifier 12. After the modulation signal Mod is inputted in the direct digital synthesizer (DDS) 13, the direct digital synthesizer 13 will process it so as to obtain a stable and reliable modulation signal to be inputted into the mixer 14. Furthermore, the mixer 14 will receive the feedback signal transmitted by the frequency divider 1, and then process it so as to directly feed the input modulation signal in the loop filter 15 in the PLL. Thereafter, a adder 16 will receive the signals outputted by the loop filter 15 and the control amplifier 12 so as to obtain a transmission signal having a higher speed and applying broad band. Then, the transmission signal is sent to a voltage controlled oscillator 17, and the voltage controlled oscillator 17 will output an emission signal to a power amplifier 3.
In the prior art, although the different modes of signals can be processed, the design has to be rearranged because of the usage of the direct digital synthesizer (DDS). The modulation loop further comprises the integrated circuits for the base band and radio frequency, and therefore, there are drawbacks for this application. Besides, because of the design method, there are drawbacks of vastly consuming electricity and occupying great area during usage. Thus, for the optimum transmission and design of the multi-mode communication system, the prior art cannot meet the needs of high-speed transmission and various functions for the service.